High Critical Current Density Research Articles

(Invited) Achieving High Areal Capacity and Extreme Critical Current Densities through Tailored Garnet Solid Electrolyte Structures

Garnet structured electrolytes are an exceptional candidate to substitute for organic liquid electrolytes owing to its high ionic conductivity and safety.[1] One of the main issues preventing the commercialization of this electrolyte is limited lithium plating capacity and lithium dendrite shorting.[2] To address this, we invented new single-phase mixed ion electron conducting (MIEC) garnet with comparable lithium-ion and electron conductivity at room temperature. We demonstrate that in a trilayer architecture, with a porous MIEC framework supporting a thin dense garnet solid electrolyte, the critical current density can be as high as 100 mA/cm2, with no dendrite-induced shorting at room temperature and without any stack pressure. The single-phase MIEC conductor spreads the potential uniformly across the material surface preventing dendrite propagation through the dense garnet solid electrolyte layer. Additionally, high lithium stripping capacity and impressive cycling stability were observed at commercial level current densities of well over 10 mA/cm2. The role of the porous MIEC garnet structure is elucidated using various electrochemical and electron microscopy techniques. Wang, C. et al. Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries. Chem. Rev. 120, 4257–4300 (2020).Albertus, P., Babinec, S., Litzelman, S. & Newman, A. Status and challenges in enabling the lithium metal electrode for high-energy and low-cost rechargeable batteries. Nat. Energy 2017 31 3, 16–21 (2017).

Electrochemical Stability of Electrode/Electrolyte Interfaces in Metal Borohydride Solid Electrolytes

Meeting the promise of all-solid-state batteries will require solid electrolytes that have high metal ion conductivity, low electronic conductivity, are electrochemically stable at both low and high potential, and have sufficiently high critical current density to avoid metal dendrite penetration. Metal borohydrides comprise a relatively new class of compounds that is being explored for its potential as a solid electrolyte material. Here, we examine the electrochemical thermodynamic stability of sodium amide borohydride (Na2NH2BH4, or NNB) over the potential range 1.5 to 5 V vs. Na/Na+, using electrodynamic methods, X-ray photoelectron spectroscopy (XPS) characterization of the interfacial reaction products1, and electron microscopy characterization of microstructure. We observe the formation of a CEI layer that passivates the NNB electrolyte up to 5V, while the electrolyte is stable without needing additional passivation down to potentials as low as 1.5V. The onset potentials of the CEI formation reactions agree with those predicted by DFT2 and suggest that the resulting CEI is composed of closo-borohydrates, which are a type of metal borohydride with a cage-like structure that holds promise for high sodium ion conductivities3. XPS measurements of atomic compositions in the CEI layer show the formation of these closo-borohydrates and, coupled with charge transfer calculations, predict that the passivating CEI layer is thin (tens of nm). Impedance spectroscopy is performed to characterize the contribution of the CEI layer to the total cell resistance. Several formation cycling methods are explored to show that with appropriate cycling, the passivating layers contribute <10% to electrolyte resistance in the test cells. Acknowledgements: This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

Oxidation in Ca/K-1144 iron-based superconductors polycrystalline compounds

Iron-based superconductors (IBSCs) are a class of material under investigation for the development of superconducting wires in the low-temperature-high magnetic fields power application. Among the various families of IBSCs, the 1144 CaKFe4As4 compound is a promising material able to achieve outstanding superconducting properties with a cheap and simple chemical composition. Oxidation, in these compounds, is considered an obstacle for high intergranular critical current density, Jc,GB. A study devoted to the evaluation of oxidation phenomena and their effects on the superconducting properties is thus needed in order to fully understand the involved mechanisms. From the evaluation of polycrystalline samples obtained by a mechanochemically assisted synthesis route, a degradation of the critical temperature and critical currents has been observed concurrently with oxygen accumulation at grain boundaries in open porosities. However, the crystalline structure at an atomic level seems not affected, as well as intragranular superconducting properties assessed by means of calorimetric methods. These results suggest that loss of superconducting properties in Ca/K-1144 compounds following oxidation is significantly associated with the worsening of grain connectivity.

Huge magnetostriction in superconducting single-crystalline BaFe1.908Ni0.092As2

The performance of iron-based superconductors in high magnetic fields plays an important role for their practical application. In this work, we measured the magnetostriction and magnetization of BaFe1.908Ni0.092As2 single crystals using pulsed magnetic fields up to 60 T and static magnetic fields up to 33 T, respectively. A huge longitudinal magnetostriction (of the order of 10–4) was observed in the direction of twin boundaries. The magnetization measurements evidence a high critical-current density due to strong bulk pinning. By using magnetization data with an exponential flux-pinning model, we can reproduce the magnetostriction curves qualitatively. This result shows that the magnetostriction of BaFe1.908Ni0.092As2 can be well explained by a flux-pinning-induced mechanism.

Dominant effect of residual secondary phase of powders on Jc and microstructure of Bi-2212 superconducting wires

Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting round wires exhibited great potential for use in high-field applications. The purity of the precursor powders is critical for the transport current of the wires. However, the role of the residual secondary phase in the precursor powders is not fully understood. Here, the origin of the secondary phase was investigated in precursor powders that were prepared using ultrasonic spray pyrolysis (USP) and calcination processing. The microstructure and phase evolution of the precursor powders during the crystallization process were analyzed. Moreover, the effects that the residual secondary phase has on melting behavior, morphology properties, and the supercurrent flow of Bi-2212 multi-filamentary wires are systematically discussed. The residual secondary phase in the filament caused further crystallization, and this led to the formation of more and larger Bi-2201 grains at the onset of the melting process. The poor microstructure and low critical current of the final Bi-2212 wires can be attributed to the presence of the residual copper-rich phase. Bi-2212 wires that were prepared with fully crystallized powders had a high critical current density (Jc) of 6773 A/mm2 at 4.2 K, self-field. It was revealed that control of the secondary phases in precursor powders is greatly significant for achieving superior values of Jc.

Anion‐tethered Single Lithium‐ion Conducting Polyelectrolytes through UV‐induced Free Radical Polymerization for Improved Morphological Stability of Lithium Metal Anodes

AbstractSingle Li+ ion conducting polyelectrolytes (SICs), which feature covalently tethered counter‐anions along their backbone, have the potential to mitigate dendrite formation by reducing concentration polarization and preventing salt depletion. However, due to their low ionic conductivity and complicated synthetic procedure, the successful validation of these claimed advantages in lithium metal (Li0) anode batteries remains limited. In this study, we fabricated a SIC electrolyte using a single‐step UV polymerization approach. The resulting electrolyte exhibited a high Li+ transference number (t+) of 0.85 and demonstrated good Li+ conductivity (6.3×10−5 S/cm at room temperature), which is comparable to that of a benchmark dual ion conductor (DIC, 9.1×10−5 S/cm). Benefitting from the high transference number of SIC, it displayed a three‐fold higher critical current density (2.4 mA/cm2) compared to DIC (0.8 mA/cm2) by successfully suppressing concentration polarization‐induced short‐circuiting. Additionally, the t+ significantly influenced the deposition behavior of Li0, with SIC yielding a uniform, compact, and mosaic‐like morphology, while the low t+ DIC resulted in a porous morphology with Li0 whiskers. Using the SIC electrolyte, Li0||LiFePO4 cells exhibited stable operation for 4500 cycles with 70.5 % capacity retention at 22 °C.

Role of electron–phonon coupling in the superconducting state of MgB2 polycrystals fabricated at different conditions

In this study, the superconducting properties of MgB2 bulk samples fabricated at different conditions were investigated. Ex situ MgB2 samples were further mixed with Mg and B at different amounts and sintered at different times and temperatures. Using Raman spectroscopy, the bearing of electron-phonon (e-ph) coupling (EPC) has been investigated. The dependence of temperature on magnetization, M(T), along with the dependence of magnetic field on magnetization, M(H), were evaluated to analyze the superconducting characteristics. Using the McMillan formular, which is modified by Allen–Dynes, and the frequency of phonon located in the mid peak centre ω2 (E2g), the contribution of EPC, whose value is closely proportional to the variation of critical temperature was reckoned. The lowest EPC value was determined by Raman spectrum analysis to be 1.094 for the MgB2 sample added with 0.5 Mg and sintered at 1000 °C for 1 h. In addition, the sample showed the lowest critical temperature along with the highest critical current density. The small bundle field (Bsb) as well as the large bundle field (Blb) were obtained using the collective pinning theory, demonstrating the expansion of the small also the large bundle regimes under suitable sample fabrication conditions. Based on the dependence of temperature on normalized critical current density (j) and normalized small bundle field (Bsb), δTc pinning is the predominant flux pinning mechanism across totally MgB2 bulk samples. The model of Dew–Hughes confirmed that the addition of Mg along with B creates surface pinning in the matrix by analyzing the pinning properties.

Sandwiched composite electrolyte with excellent interfacial contact for high-performance solid-state sodium-ion batteries

Solid-state sodium-ion batteries have attracted significant attention due to their rich resources, high safety, and high energy density. However, the lower ionic conductivity and inferior interfacial contact between solid-state electrolytes (SSEs) and electrodes limit their practical applications. Herein, polyvinylideneuoride-co-hexauoropropylene (PVDF-HFP) membrane is selected and a novel sandwiched composite PVDF-HFP/Na2.5Zr1.95Ce0.05Si2.2P0.8O11.3F0.7/PVDF-HFP (G-NZC0.05SPF0.7-G) SSEs is well designed. The ionic conductivity of Na3Zr2Si2PO12 is enhanced by Ce4+/F− co-doping. The effects of Ce4+ and F− doping on the crystal structure, density, and ionic conductivity for Na3Zr2Si2PO12 are well investigated. The optimal NZC0.05SPF0.7 delivers a high ionic conductivity of 1.39 × 10−3 S cm−1 at 25 ℃. Moreover, the PVDF-HFP membrane can significantly enhance the interface compatibility between NZC0.05SPF0.7 and electrodes. The as-prepared G-NZC0.05SPF0.7-G exhibits a large ionic conductivity of 1.07 × 10−3 S cm−1 at 25 ℃, wide electrochemical stability window up to 4.5 V, high critical current density of 1.2 A cm−2, and stable Na plating/stripping over 600 h at 0.3 A cm−2. The solid-state Na0.67Mn0.47Ni0.33Ti0.2O2/G-NZC0.05SPF0.7-G/Na battery delivers a remarkable cycling stability and rate capability at 25 ℃, indicating that the as-prepared G-NZC0.05SPF0.7-G has a promising application for solid-state SIBs. This study demonstrates an effective strategy to develop advanced solid-state electrolytes for solid-state SIBs.

Artificial Pinning Centers and the Quest of High Critical Current Densities in HTS Nanocomposites

After theoretical discovery of quantized magnetic vortices in type II superconductors by Abrikosov, which received 2003 Nobel Prize in Physics, vortex pinning has been an important topic of research for high critical current densities in applied magnetic fields desired for a variety of applications in electric and electronic devices and systems. The small vortex core size in high temperature superconductors (HTSs), of a few nanometers, has prompted an intensive research in development of nanoscale artificial pinning centers (APCs) in so-called HTS nanocomposites. Exciting results of much enhanced in-field critical current densities and pinning force densities have been achieved. This talk intends to highlight the progress made recently in HTS nanocomposites towards controllable generation of APCs with desired morphologies, dimension, concentration, and pinning efficiency for targeted applications. The future research in HTS nanocomposites to meet the need of practical applications will also be discussed.

Analyses of Deformation Due to Screening-Current-Induced Force in Layer-Wound REBCO Insert Coil for 1.3-GHz LTS/HTS NMR

REBCO wires have high critical current density and thermal stability, and are being applied in various fields such as NMR, MRI, and accelerators. We are currently designing a 1.3-GHz LTS/HTS NMR magnet that operates in a persistent current (PC) mode. However, there are issues with using REBCO coils that need to be resolved. One problem unique to REBCO coils is non-uniform electromagnetic forces caused by screening currents. During the charging and discharging of the coil, screening currents are induced, resulting in a significantly non-uniform current distribution within the coil. As a result, non-uniform electromagnetic forces are generated within the coil due to these screening currents. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this study, we performed an electromagnetic stress analysis using a two-dimensional axisymmetric structural analysis that considered tension during winding, thermal stress during cooling, and electromagnetic force during charging. First, we compared the results of the numerical simulation of the layer-wound REBCO coil with the experimental results. Then, we conducted numerical simulations of an insert REBCO coil in a design example of a 1.3-GHz NMR to evaluate the stress and deformation of the REBCO coil.

Trapped Fields of Hot-Pressed MgB2 for Applications in Liquid Hydrogen

The development of hydrogen energy and, in particular, high-performance submersible liquid hydrogen (LH) pumps requires superconducting bearings which can trap magnetic fields up to 1 T at 20 K. MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is hence a promising candidate for this application. The superconducting properties and microstructure of differently prepared MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were compared and the ability of different composite materials to trap magnetic fields was studied. Hollow cylinders of the same geometry were manufactured from hot pressed (under 30 MPa) blocks prepared from Mg:2B with Ti, TiC and Ti-O additives as well as from melt-textured YBCO ceramics. The high critical current densities and critical magnetic fields should ensure high trapped fields in all these materials. Indeed all materials demonstrated the required performance; however, flux jumps are a serious issue in MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> even in crack free cylinders and impeded higher trapped fields.

High transport Jc in 7-filament Cu/Ag sheathed Ba0.6K0.4Fe2As2 tapes manufactured by ambient pressure sintering

In regard to iron-based superconductors (IBS), the multi-filament Cu/Ag composite sheathed Ba-122 tape is particularly attractive for industrial high-field applications owing to its prominent properties. By a cost-effective and scalable way, ambient pressure sintering, a high transport critical current density (Jc) of 7-filament Cu/Ag sheathed Ba-122 tapes reached 4.5 × 104 A cm−2 at 4.2 K and 10 T, whose corresponding engineering critical current density (Je) has achieved to 104 A cm−2. An optimized powder-in-tube (PIT) method was adopted aiming at overcoming the difficulty of ambient pressure sintering to obtain high-density superconducting core and grain alignment. Improvements in the manufacturing process, such as drawing without intermediate annealing and rolling from larger initial diameter to thinner tapes, have resulted in high grain connectivity and good c-axis texture, which are the major factors contributing to high Jc. Our results demonstrate that the ambient pressure sintering process is a viable method to fabricate long-length multifilamentary Cu/Ag composite sheathed IBS tapes with high Jc for practical high-field applications.

High-Pressure Synthesis and the Enhancement of the Superconducting Properties of FeSe0.5Te0.5.

A series of FeSe0.5Te0.5 bulk samples have been prepared using the high gas pressure and high-temperature synthesis (HP-HTS) method to optimize the growth conditions for the first time and investigated for their superconducting properties using structural, microstructure, transport, and magnetic measurements to reach the final conclusions. Ex situ and in situ processes are used to prepare bulk samples under a range of growth pressures using Ta-tube and without Ta-tube. The parent compound synthesized by convenient synthesis method at ambient pressure (CSP) exhibits a superconducting transition temperature of 14.8 K. Our data demonstrate that the prepared FeSe0.5Te0.5 sealed in a Ta-tube is of better quality than the samples without a Ta-tube, and the optimum growth conditions (500 MPa, 600 °C for 1 h) are favorable for the development of the tetragonal FeSe0.5Te0.5 phase. The optimum bulk FeSe0.5Te0.5 depicts a higher transition temperature of 17.3 K and a high critical current density of the order of >104 A/cm2 at 0 T, which is improved over the entire magnetic field range and almost twice higher than the parent compound prepared using CSP. Our studies confirm that the high-pressure synthesis method is a highly efficient way to improve the superconducting transition, grain connectivity, sample density, and pinning properties of a superconductor.

Robust and Intimate Interface Enabled by Silicon Carbide as an Additive to Anodes for Lithium Metal Solid-State Batteries.

Garnet-type solid-state electrolytes are among the most reassuring candidates for the development of solid-state lithium metal batteries (SSLMB) because of their wide electrochemical stability window and chemical feasibility with lithium. However, issues such as poor physical contact with Li metal tend to limit their practical applications. These problems were addressed using β-SiC as an additive to the Li anode, resulting in improved wettability over Li6.75 La3 Zr1.75 Ta0.25 O12 (LLZTO) and establishing an improved interfacial contact. At the Li-SiC|LLZTO interface, intimacy was induced by a lithiophilic Li4 SiO4 phase, whereas robustness was attained through the hard SiC phase. The optimized Li-SiC|LLZTO|Li-SiC symmetric cell displayed a low interfacial impedance of 10 Ω cm2 and superior cycling stability at varying current densities up to 5800 h. Moreover, the modified interface could achieve a high critical current density of 4.6 mA cm-2 at room temperature and cycling stability of 1000 h at 3.5 mA cm-2 . The use of mechanically superior materials such as SiC as additives for the preparation of a composite anode may serve as a new strategy for robust garnet-based SSLMB.

Self assembled electron blocking and lithiophilic interface towards dendrite-free solid-state lithium battery

The poor interfacial contact is one of the biggest challenges that solid-state lithium batteries suffer from. Reducing the solid-state electrolyte surface energy by transforming the interface from lithiophobic to lithiophilic is effective to promote the interfacial contact, but electronic conductive interphases usually increase the risk of electron attack, thus leading to uncontrollable Li dendrite growth. Herein, we propose a self-assembled thermodynamic stable LiI interphase to simultaneously improve the interfacial contact between the garnet electrolyte Li7La3Zr2O12 (LLZO) and Li anode, and prohibit the electron attack. The direct contact between LLZO and Li and the high temperature Li melting process was ascribed to Zr4+ reduction, which facilitated Li dendrite formation and propagation. With the modification of the high lithiophilic I2 thin film, the area specific interfacial resistance of LLZO/Li was reduced from 1525 Ω/cm2 to 57 Ω/cm2. More importantly, LLZO was protected from being reduced due to the outstanding electronic insulativity of the LiI interphase, which leaded to a high critical current density of 1.2/7.0 mA/cm2 in the time/capacity-constant modes, respectively.

Mechanical properties and application of superconducting materials of Nb3Sn

Nb3Sn is one of the most promising low temperature superconducting materials and its high critical current density, high critical magnetic field strength and high critical transition temperature have attracted a lot of attention in many application areas. However, the superconductivity of Nb3Sn is strongly sensitive to its mechanical behaviour. The strain and torque arise from tension during cabling and electromagnetic forces during working operation can affect the critical performance of the strand. In this paper, the development of superconducting materials was firstly introduced in a brief way. Subsequently, the paper focused on several experiments to test the mechanical properties. Devices such as Pacman and TRASIS are used to measure the axial strain/stress, transverse force, spatial periodic contact loading cycles and periodic bending. In the next section, the paper introduced the applications and finally drew a conclusion. These results shed light on guiding future studies focusing on Nb3Sn and lay a foundation for subsequent mechanical studies of Nb3Sn.

In situ construction of a multifunctional interlayer for garnet-type electrolytes to suppress lithium dendrite formation in solid-state lithium batteries

Garnet-type solid-state electrolytes (SSEs) have great potential to be applied in all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity and excellent electrochemical stability with Li metal. However, the poor interface contact and the high electronic conductivity issues resulting in lithium dendrites growth remain challenging. Herein, we constructed a multifunctional interlayer LiF/Li-Ag alloy (LFA) in situ on the surface of garnet-type Li6.5La3Zr1.5Ta0.5O12 (LLZTO) to suppress Li dendrite growth. The matrix of the interlayer is a three-dimensional porous structure LiF and it is filled with Li-Ag alloy. The LiF blocks electron access to the LLZTO and the Li-Ag alloy ensures a good interface contact during cycling. The Li/LFA-LLZTO/Li symmetrical cells exhibit an ultralow interfacial resistance of 1.8 Ω cm2, a high critical current density of 1.1 mA cm−2 and outstanding galvanostatic cycling stability at 0.2 mA cm−2 for 2000 h. Moreover, the LiFePO4/LFA -LLZTO/Li full cell delivers a high discharge capacity of 155 mAh g−1 at 0.1 C with a capacity retention of 93% after 100 cycles.

Taming Metal–Solid Electrolyte Interface Instability via Metal Strain Hardening

AbstractSolid‐state lithium metal batteries have emerged as a promising technology for electric vehicles due to their high specific energy and safety potential. Obtaining intimate contact between Li and electrolyte during cell fabrication, however, remains challenging. Adequate fabrication pressure is required to promote close contact, but this pressure can cause Li deformation and penetration into the electrolyte, resulting in poor battery performance. Here, a strategy for addressing this problem is presented by incorporating 3 at% Mg into Li. Unlike pure Li which obeys the Voce hardening law and allows unconstrained deformation, Li─Mg alloy follows the Swift hardening law and strengthens with strain under compression stress. Because of the constrained deformation of Li─Mg, intimate contact with solid electrolytes is possible even at high fabrication pressure (50–65 MPa), resulting in high critical current densities. These findings underscore the importance of understanding Li metal deformation properties to improve solid‐state battery performance.

Electromagnetic and Thermal Analysis of HTS AC Cable using T-A Formulation

High temperature superconducting (HTS) cables have been developed into various products and attracted wide attention in industrial applications due to their high critical temperature, current density, zero resistance and overcurrent strength. Recently the triaxial YBCO cables are used in AC applications with the consideration of the flexibility and economy of materials. In this paper, the transient electromagnetic thermal characteristics of a triaxial HTS cable are analysed by the T-A formulation and the Thermal-Fluid Coupling Module of the COMSOL software under the condition of alternating current flow. Firstly, the electromagnetic T-A formulation and the basic theory of heat transfer are introduced. Transient magnetic fields, critical current distribution, and magnetization losses are discussed under T-A modelling. To evaluate the thermal behaviour of the cable under normal current conditions, liquid nitrogen laminar flow is coupled with the heat transfer module, while the heat source data are obtained from the previous T-A results.

TiO2‐Induced Conversion Reaction Eliminating Li2CO3 and Pores/Voids Inside Garnet Electrolyte for Lithium–Metal Batteries

AbstractGarnet Li7La3Zr2O12 (LLZO) is regarded as a promising solid electrolyte due to its high Li+ conductivity and excellent chemical stability, but suffers from grain boundary resistance and porous structure which restrict its practical applications in lithium–metal batteries. Herein, a novel and highly efficient TiO2‐induced conversion strategy is proposed to generate Li ion‐conductive Li0.5La0.5TiO3, which can simultaneously eliminate the pre‐existing pores/voids and contamination Li2CO3. The Li/LLZTO‐5TiO2/Li symmetric cell exhibits a high critical current density of 1.1 mA cm−2 at 25°C, and the long‐term lithium cycling stability of over 1500 h at 0.1 mA cm−2. More importantly, the excellent performance of LLZTO‐5TiO2 electrolyte is verified by LiCoO2/LiFePO4 coupled full cells. For example, The LiCoO2 coupled full cell exhibits a significant discharge rate capacity of 108 mAh g−1 at 0.1 C, and a discharge capacity retention rate of 91.23% even after 150 cycles of charge and discharge. COMSOL Multiphysics and density functional theory calculation reveal that LLZTO‐5TiO2 electrolyte has a strong lithium affinity and uniform Li ions distribution, which can improve the cycle stability of Li–metal batteries by preventing dendrite growth.